Two-band helical antenna



July 18, 1961 w. w. MACALPINE 2,993,204

TWO-BAND HELICAL ANTENNA Filed Feb. 28-. 1958 Merck/4 1,26

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LOW FREQUE/YC fill/INC; CONTROL MANUAL CONTROL E 4/0/5- 6 6. I 1 awn.7764MB- 3/N5 7 MONITOR M/TTER weal/ND Inventor WILL/AM M MACHL PINE Attorn e y 2,993,204 TWO-BAND HELI'CAL ANTENNA William W. Macalpine, EastOrange, N.J., assignor to International Telephone and TelegraphCorporation Nutley, N.J., a corporation of Maryland Filed Feb. 28, 1958,Ser. No. 718,306 8 Claims. (Cl. 343-745) This invention relates to tunedantenna systems and more particularly to a two-band tuned antennacapable of operating over a wide frequency range and utilizing aplurality of helical resonators.

In many applications it is required that the physical length of anantenna be small compared to the desired operating wavelength ofassociated transmitting or receiving equipment. It may also be requiredthat the antenna be tunable over a very wide band of frequencies andthat the standing wave ratio in the transmission line to the antenna bemaintained close to unity over the wide band of frequencies. Oneapplication where both small antenna length and wide band tuning arerequired is on surface vessels where it is preferred to employ a sturdystructure insulated from the deck to radiate as an antenna having asgreat an eifective height as possible. In such application the height ofthe structure is limited for practical reasons and it is preferable thatthe structure be resonated by some means that is tunable over a wideband of frequencies.

Heretofore helically top-loaded and capacitive toploaded antennas havebeen employed to extend the effective electrical length of a radiatorwithout adding appreciable physical height. The helical resonatorsemployed in such antennas as top-loading have also been designed foroperation over a wide frequency range by incorporating various methodsof electrically shorting portions of the helical resonator and/ orvarying the capacitive toploading members coupled to said helicalresonators. It has also been the practice in the past to vary the pointof input coupling to helically top-loaded radiators to improve impedancematching.

An object of this invention is to provide a tuned antenna system of highefficiency wherein the physical height of the radiator extending abovethe ground plane varies only slightly.

Another object of this invention is to provide a wide band tuned antennasystem employing helical resonators.

Another object is to provide a helical antenna system which can bereadily tuned over a wide band of frequencies.

Another object is to provide a tuned helical antenna system to extendthe electrical length of a structure so as to make it resonant over awide band of frequencies.

In accordance with a feature of this invention, the electrical length ofa radiating body is varied to tune said body over a wide range offrequencies by coupling a plurality of helical resonators, one disposedabove the other, to said body and providing means to vary the activeportions of said helical resonators.

It is another feature of this invention to provide an adjustableshorting device to vary the active portion of one of said helicalresonators for lower frequency tuning and to employ a second adjustableshorting device to vary the point of coupling of the capacitive toploading to the outermost of said helical resonators for higher frequencytuning and to provide different motor means to drive said firstadjustable device and said second adjustable device.

Other and further objects and features of this invention will be moreapparent by reference to the following description taken in conjunctionwith the accompanying drawing which is a side view of one embodiment ofa Patented July 18, 1961 "ice 2 two-band helical antenna in accordancewith the principles of this invention.

Referring to the figure, there is shown a structure 1 disposedvertically above and insulated from a ground plane 2 by severalinsulators of which two are shown at 3 and 4. In the embodiment shown inthe figure, the structure is employed to radiate energy; therefore,power from transmitter 5 is applied via coaxial line 6 to an impedancematching coil 7 which couples the bottom of structure 1 to ground withmanual control means 8 being provided to vary the portion of coil 7across which the input line is shunted. On top of structure 1 andelectrically connected thereto is low frequency helical reso nator 9,and disposed above resonator 9 and electrically coupled thereto is highfrequency helical resonator 10 having top-loading capacitive member 11disposed above and connected electrically thereto by means of springfingers 12 which are arranged in a circle so as to provide positiveelectrical connection between capacitive member 11 and resonator 10 ascapacitive member 11 is caused to move up and down by the rotary actionof dielectric shaft 13 which is mechanically linked to high frequencytuning motor 14. Adjustable shorting shield 15, preferably ofcylindrical shape and concentric with resonators 9 and 10, is providedwith shorting spring fingers 16 at its bottom end which makes positivecontact with resonator 9 as shorting shield 15 moves up and down withrespect to resonators 9 and 10. Spring contact fingers 17, fastened toconductive coupler 18 which electrically connects resonator 9 toresonator 10, make positive contact with shorting shield 15 as theshield moves up and down with respect to fingers 17. Shorting shield 15is caused to move up and down by the simultaneous rotary motion ofdielectric rods 19 and 20 which are mechanically linked via gear boxes21 and 22, respectively, to low frequency tuning control motor 23. Thethreaded portions of rods 13, 19 and 20 can be of metal. However, thepart of rod 13 which is within helices 9 and 10 must be of dielectricmaterial because of the powerful magnetic fields within helices 9 and10. similarlyithere must be a portion of rods 19 and 20 that is made ofdielectric material due to the difference of electrical potentialbetween shield 15 and the structure at gear boxes 21 and 22.

In operation the structure 1 is energized by transmitter 5 via coaxialline 6 and coil 7 causing an indication on standing wave ratio monitor24. Depending upon the output frequency of transmitter 5 and initialpositionsof capacitive member 11 and shorting shield 15, high frequencytuning motor 14 or 'low frequency tuning motor 23 can be energized asdescribed below. If it is desired to tune structure 1 in the lowfrequency range, say, for example, between 300 kc. and 3 mo, lowfrequency tuning motor 23 will be energized from low frequency tuningcontrol device 25 which may be merely a switch providing positive,negative or no electrical energy to motor 23. Upon energizing motor 23,standing wave ratio monitor 24 is observed by an operator who willoperate control device 25 causing shorting shield 15 to move upwards ordownwards until the standing'wave voltage ratio in transmission line 6,as indicated by monitor 24, reaches a minimum. The standing wave ratiofound in the above tuning process becomes a minimum when the antenna isresonant; thus, manual control 8 can now be adjusted to change theimpedance match and further reduce the standing wave ratio toward itsoptimum value of unity. Frequently little or no adjustment of control '8is required, and in many cases manual control Scan'be eliminatedentirely by providing the proper size of coil 7 and connecting thecoaxial line 6 across the entire coil 7. As the antenna system shown inthe figure is tuned'to 3 higher and higher frequencies in the lowfrequency range, shorting shield 15 will be driven downward until contact fingers 16 reach the bottom of resonator 9. Fine adjustment of thetuning in the low frequency range can -be accomplished, if desired, bycontrolling the position of capacitive load 11 with its contactfingers'12 on the smaller helix 10 by means of motor 14 and high frequencytuning control 26. Subsequently, further tuning to still higherfrequencies in the high frequency range, say, for example, between 3,mc.and 30 mc., will be accomplished by energizing high frequency tuningmotor 14 from high frequency tuning control device 26 which may bemerely a switch applying positive, negative or no electrical energy tomotor 14. Motor 14'drives dielectric shaft 13 which is threaded at itsupper end, in contact with top-loading capacitance 11, so that as shaft13 turns one way or the other, top-loading capacitive member 11 iscaused to move upwards or downwards to increase or decrease the resonantfrequency of the antenna device in the'high frequency band. The operatorcontrols high frequency tuning in the same manner he controls lowfrequency tuning, namely, by observing standing wave ratio monitor 24and actuating the appropriate tuning control device 26 and furtheradjusting manual control 8 until the standing wave ratio in transmissionline 6 is a minimum. In most applications where very wide band tuning isdesired, high frequency range tuning is achieved in steps, the firststep being to resonate the system at a quarter wavelength (M4) over arange of As, say from 3 me. to 9 mc., by moving capacitance 11 from itstop to its bottom position, the second step being to resonate the systemat 3M 4 over the range of roughly 9 me. to 15 me. or higher, the thirdstep being to resonate at 5A4 over the range of roughly 15 me. to 30 mo.and so forth, until the system is tuned over the range desired. Itshould be observed that, while tuning in the high frequency range bymeans of resonator 10, the low frequency resonator 9 is completelyisolated and shielded by means of shorting shield 15, conductive coupler18 and the conductive coupler 27 shown at the base of resonator 9. Forthis reason conductive couplers 18 and 27 are solid metal disks exceptfor a smal opening in each to accommodate dielectric shaft 13 and suchstructural bolts as may be required. Thus the natural resonantfrequencies of resonator 9 are inhibited from influencing the tuning ofresonator 10.

While in the specific embodiment described hereinabove I have shown thatboth helices are positioned at the top of the structure 1, it is alsopossible to separate the helices and position them at different pointsalong the structure.- One satisfactory arrangement is to place the highfrequency helix beneath the structure 1, for example, in place of coil 7and similarly connected to coaxial line 6 while leaving the lowfrequency helix 9 in the position indicated in the drawing. In thisarrangement,-the helix 9 will serve to resonate the structure in the lowfrequency range thus giving a substantially uniform current distributionalong the structure for that range. For the frequencies of the highfrequency range, the structure may, by itself, be sufficiently long toserve as an eflicient radiator if the tower is electricallyapproximately one eighth to three quarter wavelengths long. Tuning ofthe high frequency helix may be performed by shorting out parts of itwhile impedance matching may be performed by selecting the point on saidhelix to which the coaxial line is coupled.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

Iclaim:

' 1. A radio antenna system comprising a vertical radiating member, aplurality of helices mounted one above thecther on said member insubstantial vertical alignment therewith said plurality of helicesdisposed in tandem relationship with each other and said. vertical.radiating member so that the cylinders formed by said helices do notoverlap, the bottom and the top of adjacent helices of said plurality ofhelices being electrically coupled in a series relationship, and thebottom of the lowest helix of saidplurality of helices beingelectrically coupledto the top of said member each of said heliceshavinga different diameter, each of said helices having a differentelectrical length, means for shorting out a selectable amount of theelectrical length the lower one of said adjacent helices of saidconnected helices of said shorting means including a shielding member toprevent undesirable coupling between said plurality ofhelices to tunesaid radiating member over a given frequency range, and variable meansfor shorting out a selectable amount of the electrical length of theupper one of said adjacent helices of said series connected helices totune said member over a second frequency range.

2. A radio antenna system according to claim 1, where in said upper oneof said adjacent helices of saidseries connected helices has a shorterelectrical length than said lower helix of said adjacent helices of saidseries con nected helices and its shorting means tunes said member overa higher frequency range while the shorting means of said lower helix ofsaid adjacent helices of said series connected series tunes said memberover a lower frequency range.

3. A radio antenna system according to claim 2, wherein the shortingmeans for said upper one of said adjacent helices of said seriesconnected helices is in the form of a shorting housing providingcapacitive loading.

4. A radio antenna system comprising a first radiating member coupled atone end to a transmissionline, a first posed at one end'of said secondhelical member and coupled thereto in a variable manner, and controlmeans mechanically coupled to said shorting means and said capacitivemember to adjust them and to tune said radiating member over a widerange of frequencies.

5. A radio antenna system as in claim 4 and wherein said adjustableshorting means further includes shielding means to shield varyingportions of said second helical member as said adjustable shorting meansis adjusted.

6. A radio antenna system comprising a radiating structure insulatedfrom ground and coupled to a transmission line at its one end, a firsthelical member having its one end electrically coupled to the other endof said structure, a second helical member having its one end connectedto the other end of said first helical member and disposedconcentrically above, adjustable top loading coupled to the other end ofsaid second helical member, adjustable shorting means coupling said one.end of said second helical member to said first helical member, firstmotor means coupled to said shorting means, second motor means coupledto said top loading, and means to control said first and second motormeans to tune said system over a wide band of frequencies.

7. A radio antenna system as in claim 6 and wherein said adjustableshorting means further includes shielding means coupled thereto toshield a varying portion of said second helical member as saidadjustable shorting means is adjusted.

8. A radio antenna system comprising a vertically disposed structureinsulated from ground and coupled to a transmission line by variableshunting means at one end of said structure, a low frequency helicalresonator vertically disposed and coupled to the other end of saidstructure, a high frequency helical resonator vertically disposed'aboveand coupled to said low frequency helical resonator, adjustabletop-loading capacitive means coupled to said high frequency helicalresonaton adjusta able shorting means coupling the interjunction of saidhelical resonators to a variable number of turns of said low frequencyhelical resonator having shielding means attached thereto for shieldinga variable number of turns of said high frequency helical resonator assaid shonting means is adjusted, first motor means coupled to saidtoploading capacitance, second motor means coupled to said adjustableshorting means, and control means associated with each of said motormeans, the general arrangement of said system being such that said motormeans may be energized to tune said system over a wide range offrequencies.

References Cited in the file of this patent UNITED STATES PATENTS VanceMay 30, 1933 Nickle Aug. 2, 1938 Roosenstein Feb. 16, 1943 Sichak et al.Feb. 12, 1957 Taylor et al. Sept. 30, 1958 Kandoian Oct. 7, 1958Kandoian Dec. 23, 1958 Kandoian Feb. 24, 1959

